The present invention relates to antifog films useful for packaging food, and more particularly to printed antifog films having an improved ability to maintain antifogging characteristics after being rolled.
Refrigerated food items are often displayed to consumers by resting the food item in a tray and covering the top of the tray with a transparent plastic film wrap. Typically, the food tray will have a perimeter lip extending above the stored food item so that the plastic film covering the top of the tray does not touch most of the packaged food. In this arrangement, the consumer may see clearly through the plastic wrap to view the food item stored in the package.
Upon refrigeration of a food item packaged in this manner, a xe2x80x9cfogxe2x80x9d may form on the inner, food-contact or food-side of the film, especially if the packaged food item has a high-moisture content. The term xe2x80x9cfogxe2x80x9d describes the collection of small moisture droplets that condense on the inner side of the film wrap. Unfortunately, these water droplets may cloud the inner surface of the film and thus obstruct or disrupt the view through the filmxe2x80x94resulting in a negative consumer perception because of the inability to see clearly the packaged food through the plastic film wrap.
There have been several approaches to reduce the negative effects of fogging. One approach involves dispersing one or more antifog agents in the plastic film resin during processing of the film. Once in the film resin, the antifog agent tends to migrate to the surface of the film and raise the surface tension of the film. As a result, the water on the film inner side tends to form a relatively continuous film-like, transparent sheet of water rather than a fog.
Another approach to minimize the negative effects of fogging on a film involves applying an antifog coating directly to the plastic film""s inner, food-side surface. Although this approach adds the expense of an additional coating step, it provides the benefit of applying the antifog agent to the film surface where it is most effective at reducing fogging.
A plastic film wrap typically includes printed regions on the film""s outer surface to provide the consumer with visual information. The ink is printed to the outer, non-food side of the film to avoid contacting the packaged food with the print ink.
For the convenience of the packager, anti-fog packaging films are often supplied in pre-printed roll form. When the printed film is wound about a central core in progressive layers to form a roll, the printed side of the film contacts the non-printed side of film. This rolled arrangement causes surface contact between the film""s printed outer side and the film""s non-printed inner side. This contact appears to reduce the antifog effectiveness of the antifog film in the areas where the inner, food-side surface of the film has contacted the printed region of the film""s outer surface.
As a result, when a packager unrolls a printed antifog film, wraps a food tray containing a food product, and refrigerates the packaged food product, a fog may form on the inner side of the film corresponding to the area of the inner surface that had been in contact with the printed region of the outer film surface when the film was rolled. Yet, where the film""s inner surface area did not contact the printed regions when the film was rolled, the antifog film appears to function as designedxe2x80x94that is, reduces the formation of fog. The term xe2x80x9cghostingxe2x80x9d refers to this contrast between transparent areas in which the antifog functions as designed and the opaque area in which a fog formsxe2x80x94because the fogged area on the film""s inner surface may form a xe2x80x9cghost imagexe2x80x9d of the printed area on the film""s outer surface.
The aforementioned problems are overcome in the present invention wherein a printed plastic antifog packaging film incorporates one or more organic acid esters of cellulose to reduce the tendency of the film to form a ghost condensate image of the printed image.
In a first aspect, the cellulose ester resin is incorporated in the ink that forms the printed image of the antifog packaging film. Accordingly, the printed packaging film includes an antifog film having first and second sides. At least the first side of the film has an antifogging characteristic. A printed image is on at least a portion of the second side of the film. The printed image includes an ink having an effective amount of one or more organic acid esters of cellulose.
In a second aspect of the invention, the cellulose ester resin is incorporated in an overprint varnish that covers the printed image of the antifog film. Accordingly, the printed packaging film includes a plastic film having first and second sides. At least the first side of the film has an antifogging characteristic. A printed image is on at least a portion of the second side of the film. An overprint varnish is on at least a substantial portion of the printed image. The overprint varnish includes an effective amount of one or more organic acid esters of cellulose.
The printed packaging film of the present invention presents several advantages. The film displays a reduced tendency for forming a ghost condensate image of the printed image after the film has been rewound to form a roll, and subsequently unwound for use in packaging that is exposed to conditions that form a moisture condensate on the film. The film thus provides a protective covering for a refrigerated packaged food itemxe2x80x94for example, a refrigerated meat product on a trayxe2x80x94yet allows the consumer a pleasing, clear view of the stored food product without the disruption of a ghost condensate image. The printed antifog film may be manufactured using conventional equipment, for example either by including the cellulose ester resin in the ink layer that is applied in the final station of a print process or by including the cellulose ester resin in an overprint varnish that is applied in the final print station. The printed antifog film also displays excellent print adhesion and gloss properties.
These and other objects, advantages, and features of the invention will be more readily understood and appreciated by reference to the detailed description of the invention and the drawings.